Gas operated firearm

ABSTRACT

A belt fed, gas fired machine gun has its gas port located just forward of the firing chamber so that the weight of its associated cylinder and piston is concentrated towards the rear of the gun. Power for operating the bolt, firing pin hammer and ammunition feed is stored in springs opposing movement of the piston in response to the gas firing pressure. The bolt has longitudinal movement only and is locked in chambered position by a cam actuated rotary latch which also performs the triggering function when the gun is operated in the full automatic setting. Interlinked ammunition is fed transversely through the gun by reciprocal tray pieces which are actuated by leaf springs whose return movement is imparted by return of the bolt to its chambered position. Vertically slidable sear plates latchably control the firing pin hammer, which is mounted telescopically within the bolt. The gun is assemblable for either right or left hand operation.

United States Patent [191 Donovan [4 Dec. 4, 1973 GAS OPERATED FIREARM [22] Filed: Oct. 21, 1971 [2]] Appl. No.: 191,297

Primary Examiner-Stephen C. Bentley Attorney-Gerald E. McGlynn, Jr.

[57] ABSTRACT A belt fed, gas fired machine gun has its gas port located just forward of the firing chamber so that the weight of its associated cylinder and piston is concentrated towards the rear of the gun. Power for operating the bolt, firing pin hammer and ammunition feed is stored in springs opposing movement of the piston in response to the gas firing pressure. The bolt has longitudinal movement only and is locked in chambered position by a cam actuated rotary latch which also performs the triggering function when the gun is operated in the full automatic setting. Interlinked ammunition is fed transversely through the gun by reciprocal tray pieces which are actuated by leaf springs whose return movement is imparted by return of the bolt to its chambered position. Vertically slidable sear plates latchably control the firing pin hammer, which is mounted telescopically within the bolt. The gun is assemblable for either right or left hand operation.

20 Claims, 40 Drawing Figures PATENTEDDEB 4m 3776096 SHEET 10F 8 I N VENTORQ ATTO RNEYS "MFNIFHUHI 41975 3775-096 SHEET 6 CF 8 I N VEN TOR.

ATTORNEY l GAS OPERATED FIREARM BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to fire arms of the gas fired semi-automatic and automatic type, and particularlyto improved actuating means therefor. Prior manually held guns of this type have tended to be of a design in which the gas actuating pressure is taken from a port in the barrel located a considerable distance forwardly of the firing chamber, in many cases just rearwardly of the muzzle. As a consequence, weight of the gas power cylinder lies well forward of the trigger and the stock or other supporting portion of the gun, resulting in loss of needed weight concentration to obtain optimum balance for mitigating firing inertia force. Exemplary of such prior art arrangements are those disclosed in U.S. Pat. No. 784,966 Smith, 1,010,899 l-lalle, 1,019,620 Farquhar et al., 1,786,207 Hudson, 2,101,862 Mac- Gregor, 2,386,205 Garand, 2,975,679 Fletcher, 2,981,158 Fletcher and 3,318,192 Miller. The gun of my invention avoids this problem by having the gas port located just forwardly of the firing chamber so that the gas cylinder and its piston may be made relatively short and the weight thereof concentrated closer to where the gun is supported.

Also, while it is old in the prior art, as for example in the aforementioned I-Ialle, Farquhar et a1. and Mac- Gregor patents, to employ the gas pressure to build up a spring force to actuate the bolt, I believe I am the first to utilize a plurality of springs which initially operate in parallel to absorb the gas pressure force and thence serve sequentially to actuate the bolt latch, power the retraction of the bolt, recocking of the hammer and trigger controlled sear mechanism, the re-chambering of the bolt, as well as the feeding of ammunition and ejection of spent cartridges.

Also the bolt is of unique design in that it co-axially mounts the firing pin and hammer, the hammer having a rearward stem portion extending beyond the rear end of the bolt for engagement with a vertically slidable sear which is releasable by a selectively manually or automatically actuatable rod.

Another unique feature of my gun lies in the bolt latch which operates rotatably about the longitudinal axis of the bolt and is cammed to the unlatched position by a member driven by the gas piston. I also provide a novel ammunition feeding arrangement wherein a belt of interlinked cartridges is passed horizontally through the gun by reciprocating members which grip successive belt links, the reciprocation being imparted by side mounted spring fingers whose return movement is actuated by the return movement of the bolt.

The means by which these and other advantages and improvements are attained will be understood from the following description of a preferred embodiment selected to best illustrate the invention, having reference to the drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 are left side, right side and top elevational views, respectively, of a machine gun embodying the invention.

FIG. 4 is a longitudinal vertical section taken substantially along the line 4-4 of FIG. 3, certain parts being shown in elevation and only the rear portion of the barrel being illustrated;

FIG. 5 is a longitudinal horizontal section taken substantially along the line 5-5 of FIG. 1, certain parts being shown in elevation;

FIGS. 6 and 7 are transverse cross sections taken substantially along the lines 6-6 and 7-7, respectively, of FIG. 5.

FIG. 8 is a partial horizontal section taken substantially along the lines of 8-8 of FIG. 4.

FIG. 9 is a perspective view of the ammunition feed upper and lower spring fingers, shown removed from the assembly.

FIG. 10 is a perspective view of the gas power cylinder and its integral mounting ring, shown removed from the assembly.

FIG. 11 is a transverse cross section taken substantially along the line 11-11 of FIG. 4.

FIG. 12 is an end elevational view of the snap ring, shown removed from the assembly.

FIG. 13 is a side elevational view of the buffer member, shown removed from the assembly.

FIG. 14 is a horizontal longitudinal section of the buffer member, taken substantially along the line 14-14 of FIG; 13.

FIG. 15 is a front end elevational view of the buffer member, taken in the direction of the arrows 15-15 of FIG. 13.

FIG. 16 is a side elevational view of the housing, shown removed from the assembly.

FIG. 17 is a front elevational view of the housing, taken in the direction of the arrows 17-17 in FIG. 16.

FIGS. 18, 19 and 20 are transverse sections of the housing, taken substantially along the lines 18-18, 19-19 and 20-20, respectively, of FIG. 16.

FIGS. 21, 22 and 23 are perspective views of one of the feed trays, the buffer locking spring, and the bolt latch, respectively, shown removed from the assembly.

FIG. 24 is a partial side elevational view of certain interrelated parts of the triggering mechanism, as viewed from the left side of the gun, the parts being in their safety condition.

FIGS. 25 and 26 are perspective views of the trigger and trigger rod actuator, respectively, shown removed from the gun.

FIG. 27 is a partial side elevational view similar to FIG. 24, but showing the parts of the triggering mechanism at the stage of operation intermediate the depression of the trigger and the releasing of the bolt latch, the gun being operated in the full automatic mode.

FIGS. 28 and 29 are partial elevational views, looking rearwardly and downwardly of the gun, respectively, showing the parts of the triggering mechanism under the same condition as in FIG. 27. 7

FIG. 30 is a view similar to FIG. 29, but showing the relative position of the parts therein after the bolt latch has moved to its bolt released position.

FIG. 31 is a view similar to FIG. 24, but showing the parts of the triggering mechanism with the gun arranged for operation: in the semi-automatic mode.

FIGS. 32 and 33 are perspective views of the front and rear seat plates, respectively, shown removed from the gun.

FIGS. 34a, 34b, 34c, and 34d are diagrammatic views showing the action of the trigger rod and'upper and lower sear springs in controlling the latching and unlatching of the hammer by the front and rear sear'plates during operation of the gun in the semi-automatic mode.

FIG. 35 is a partial elevational view of the trigger guard and hand grip, showing the finger lever in solid lines in its position for operating the gun in the full auto-matic mode, and in dashed and dash-dot lines in its semi-automatic mode" and safety positions, respectively.

FIG. 36 is a diagrammatic plan view of a portion of the ammunition belt, with the relative positions of the feed trays indicated in broken outline.

FIG. 37 is a diagrammatic end elevational view of a portion of the ammunition belt, taken in the direction of the arrows 37-37 of FIG. 36, with the relative positions of the feed trays indicated in broken outline.

DESCRIPTION OF THE PREFERRED EMBODIMENT General Arrangement The embodiment of the invention illustrated in the drawings is a machine gun adapted to be hand held and to fire shells of approximately 30 caliber, the shells having their cartridges extending through aligned loops of adjacent cartridge links which are thus interconnected by the cartridges to form an ammunition belt which passes through the gun during operation. It should be appreciated, however, that many of the novel constructional features of the gun could be applied to the firing of either larger or smaller bore shells, as well as to socalled automatic guns having magazine type ammunition feeding arrangements. Also, while the gun is disclosed as selectively operable either in a full automatic mode (continuous firing while the trigger is maintained depressed) or in a semi-automatic mode (firing one shell with each successive depression of the trigger), many of its features could be applied with equal advantage to manually operated bolt guns of the single shot type.

FIG. 1 shows the external appearance of the gun as viewed from the left side, with the barrel 1 extending forwardly from the stock portion, indicated generally by the numeral 2, which terminates rearwardly in a shoulder butt 3 and intermediate its ends has a depending trigger guard and hand grip 4.

It should be mentioned at this point that certain hereinafter described parts associated with the stock portion 2 are reversible in respect to their orientation in the assembly, enabling the gun to be alternatively assembled for most convenient operation by either a right handed" user or a left handed user. Only the former, or R.I-I. form of assembly, however, is illustrated in the drawings. FIG. 1 shows the entrance ends of the upper and lower feed trays 5 and 6, between which the ammunition belt (not shown) passes in its horizontal movement transversely through the gun. The external appearance of the gun as viewed from the opposite, or right side, is shown in FIG. 2, the exit ends of the ammunition belt feed trays 5 and 6 being visible therein, as well as the laterally projecting handle 7 for manually operating the bolt. FIG. 3 shows the external appearance of the gun as viewed from above, with the barrel 1 extending to the left as in FIG. 1.

Housing and Firing Chamber Referring now to FIGS. 4 and 5, the main supporting frame for the stock portion 2 is provided in the form of a housing 8. This housing extends rearwardly the full length thereof to the butt 3, and its front end has a forwardly open counter bore 9 into which the rear portion of the barrel has a close slip fit. The barrel is retained against the shoulder 10 at the rear end of this counter bore by a normally expansible snap ring 11 having dual interengagement with an external groove on the barrel and an internal groove in the counter bore 9. The bore 12 in the barrel terminates at its rearward end in a firing chamber 13, in which a live" ammunition shell 14 is shown ready for firing.

Power Cylinder and Buffer Member A short distance forwardly of the firing chamber, the barrel is provided with an upwardly extending port 15 which connects its bore 12 with a connecting passage 16 leading into the forward end of the bore 17 of a gas power cylinder 18. This power cylinder extends rearwardly along the top of the housing 8, being seated thereon in the upper of two longitudinal grooves provided in the top and bottom of the housing which are best shown in FIGS. 17, 18 and 19. Slidably supported in a rear counter bore 19 of the housing for reciprocation rearwardly of the power cylinder is a generally tubular shaped bufler member 20. Integral with the forward end of this buffer member are upwardly and downwardly extending arms 21 and 21 and the laterally extending manual operating handle 7, which project through respective longitudinal slots provided therefor in the top, bottom and side walls of the housing rear counter bore 19. A rod like piston 22 is provided in the bore 17 of the power cylinder 18 for effecting rearward movement of the buffer member in response to the gas explosion pressure developed in the firing chamber 13 when the shell 14 is fired. The rear end of this piston pilots in a through hole provided in the upper arm 20 of the buffer member, and the rear end of the power cylinder is counter bored to receive a flange or collar portion 23 on the piston which serves both to limit return (i.e., forward) travel of the piston and to provide a thrust connection between the piston and the buffer member upper arm 21.

Spring Chambers The upper and lower arms 21 and 21' of the buffer member are enclosed in respective upper and lower spring chambers 24, 25 which extend rearwardly along the top and bottom of the housing 8 to the butt 3. Within the upper spring chamber 24 and interposed in thrust between the upper arm 21 and the butt is a coil compression spring 26. Slidably shiftable within the lower spring chamber 25 is a spring retainer 27 having a rear end wall, and interposed in thrust between this wall and the lower arm 21' of the buffer member is a coil compression spring 28. Extending freely through this spring and slidably piloted in through holes in the buffer member lower arm 21 and the reatainer end wall is a trigger rod 29. This trigger rod extends forwardly a short distance beyond the forward end of the lower spring chamber 25 and terminates within the trigger guard and hand grip 4. The rear end of the trigger rod, as best shown in FIG. 8, has a bifurcated or yoke like portion 30 with laterally spaced arms 31 and 32 extending into the butt 4 and terminating in downwardly and rearwardly inclined ramp surfaces 33 and 34, respectively.

Bolt

Slidably guided for reciprocation in a bore 35 of the housing, between the counter bores 9 and 19, is a bolt 36. In its forward or closed position, as shown in FIGS. 4 and 5, the bolt 36 serves the conventional functions of chambering the shell 14 and providing the retention means for the gas pressure force which is released when the explosive charge in the cartridge 37 of the shell is detonated. Axial rotation of the bolt in the housing is prevented by upper and lower ribs 38 "and 39'on the bolt which have close sliding engagement with longitudinally extending upper and lower grooves 40 and 41 in the housing bore 35. The bolt ribs 38'and 39 extend a short distance forwardly of the main body of the bolt and are turned inward toward each other to form lugs 42 and 43 for an interengagement with the usual extraction groove 44 on the rear end of each shell cartridge. A short distance forwardly of their rearward end the respective bolt ribs 38 and 39 are interrupted by grooves or notches 45 and 46, and joumalled on the bolt within these notches is a rotary latch 47. The bolt bore 35-and the rib receiving upper and lower grooves 40 and 41 are also interrupted intermediate their ends by a horizontal passageway or slot 48 extending transversely through the housing 8. Adjacent its rearward end this slot provides clearance for the outer periphery of the latch 47, and the portion of the slot extending forwardly of the latch accommodates reciprocation of the upper and lower feed trays 5 and 6. It will be understood that the latch is supported against axial displacement in the rearward direction by the upper and lower rear end walls of the slot 48 in the housing, and that the upper and lower front end walls of this slot and the front face of the latch cooperate in locating the feed trays longitudinally of the housing. At its forward end, this slot 48 connects with other transverse slots, to be later described.

Firing Pin The bolt 36 has a small axial bore 54 extending through its forward end for projection of a firing pin 55 to detonate the charge in the cartridge 37. Extending coaxially and rearwardly of this small bore is a counter bore 56 in the bolt in which the main body portion of the firing pin is slidably supported, and in the forward end of this counter bore is a coil spring 57 for biasing the firing pin into its normally retracted position, shown. A longitudinal groove 58 in the main body portion of the firing pin cooperates with a pin 59 projecting therein from one side of the bolt to limit the rearward movement of the firing pin under the biasing force of the spring 57.

Hammer Extending coaxially and rearwardly to the rearmost end of the bolt from the counter bore 56 is a larger counter bore 60 into which the rear end of the firing pin 55 protrudes, and in which a hammer 61 is slidably supported. The hammer has a rearwardly extending stem 62 which is slidably guided in a central aperture 63 provided in a nut 64 shown threadably secured to the rear end of the bolt. A coil compression spring 65 encircles the stem 62 and is interposed in thrust between the nut 64 and the hammer, so as to bias the hammer into striking engagement with the rear end of the firing pin. The stem 62 has an enlarged rear end portion 66 with a rearwardly facing frusto-conically shaped end face 67, the outer extremities of which terminate in a forwardly facing shoulder or latching face 68.

Sears Sear means, in the form of front and rear vertically shiftable sear plates 69, 70 and upper and lower biasing spring 71, 72, is provided for latchably interengaging the end portion 66 of the hammer. When thus latched, the hammer is held in its cocked position shown in FIGS. 4 and 5. The sear springs 71, 72 as indicated in FIG. 4, may be in the form of single leaf cantilever springs with their forward ends held fixed to the butt by rivets 73, 74. Both sear plates are biased downwardly by the rearwardly extending free end of the upper sear spring 71, but the lower sear spring 72 applies its upward biasing force only against the rear sear plate 70. Also, both sear plates have central openings therein to accommodate passage therethrough of the hammer end portion 66, the upper edge of such opening in the front sear plate and the lower edge of such opening in the rear sear plate being preferably chamfered, as indicated at 75 and 76 in FIG. 4, to conform with the angle of the frusto-conical face 67. The lower end face of the front sear plate is likewise chamfered, as indicated at 77 in FIG. 4, to conform with the angle of the ramp faces 33 and 34on the rearward extremities of the trigger rod 29.

Bolt Retracting Spring Encircling the portion of the bolt 36 extending'into the buffer member 20 is a coil compression spring 80 which is interposed in thrust between the nut 64 and an inturned flange 81 on the forward end of the buffer member. Pending release of the bolt by the rotary latch 47, this spring 80 thus applies increasing bias tending to retract the bolt rearwardly from its chamber closed position shown in FIGS. 4 and 5, as the buffer member is driven rearwardly, from its position shown, by the piston 22.

Bolt Latch The latch 47, as best shown in FIG. 23, has a main body portion with a part circular bore 82 extending axially therethrough, and an angularly depending leg portion from which a finger 83 extends in spaced and partially encircling relation about the lower periphery of the main body portion. The bore 82, which serves to rotatably pilot the latch on the bolt, is interrupted by diametrically opposite key ways 84, 85 for accommodating passage of the bolt ribs therethroughwhen the latch is rotated into registry therewith. On the outer periphery of the main body portion of the latch is a groove 86, one end of which'connects with a drilled hole 87 extending through the angularly depending leg portion of the latch.

Latch Spring As best seen in FIG. 7, thislatch groove 86 and drilled hole 87 serve to recess a generally U-shaped wire spring 88, the upper leg of which reacts against the upper wall 89 of the housing slot 48 and causes the lower leg to rotatably bias the latch in a clockwise direction about the bolt 36. Such rotation is limited by the lower tangentially extending portion 90 of the latch periphery striking the bottom wall 91 of the housing slot 48, the latch then being in its bolt closed position in which its key ways 84, 85 are out of alignment with the bolt rib 38, 39 and the .latch finger 83 is approximately centered circumferentially about the underside of the housing. The latch biasing spring 88, while normally retaining the latch in such bolt closed position shown, will yieldably accommodate counterclockwise rotation of the latch to its bolt released position in which the key ways 84, 85 are aligned with the bolt ribs 38, 39. Such counter rotative movement is resisted by the upper leg of the latch spring becoming :further wrapped about the grooved periphery of the latch body, and is arrested at the bolt released position by the upper tangentially extending portion 92 of the latch periphery striking the upper wall 89 of the housing slot 48.

Latch Actuating Cam A cam member 93 is provided for actuating the latch to its bolt released position. As best seen in FIG. 8, this comprises a generally triangular shaped cam nose portion 94 extending transversely and located mid length of a rod 95. At the opposite ends of this rod are short arms 96, 96', each with a hook forming notch 97 facing each other, and equally spaced somewhat fore and aft of the nose portion 94 are provided a second set of short arms 98, 98. All four of the arms 96, 96', 98, 98 and the nose portion 94 extend in the same transverse direction, and each thereof, as well as the rod 95, is arcuate shaped in transverse section to conform to the curvature of the underside of the housing 8 (FIGS. 6 and 7). The nose portion 94 has oppositely facing lobes 99, 99, of which only the rearwardly facing lobe 99 is functional in the gun as assembled for right handed operation. The rearmost arm 96 projects through an elongated slot 100 provided therefor in the right sidewall of the lower spring chamber 25. Opposite sidewalls of the spring retainer 26 are provided with apertures 101, 101 adjacent their forward end, and the notched end of cam member arm 96 extends into the right sidewall aperture 101 of this spring retainer. The longitudinally extending upper wall 102 of the finger guard and hand grip 4 supports the forward portion of the cam member 93, and is arcuate shaped in transverse section (FIG. 6) to conform to the curvature thereof. In the gun as assembled for right handed operation, the cam member arm 98 projects through a longitudinal slot 103, provided in the forward portion of the lower spring chamber right sidewall, and extends into abuttable engagement with the front face of the buffer member lower arm 21 The cam member 93, including its rod 95, arms 96, 96', 98, 98' and a portion of the cam nose portion 94, are also visible in FIG. 4.

Feed Spring Fingers When the bolt 36 is retracted, the upper and lower feed trays and 6 are shifted in a rightward direction, to the broken line position 104 shown in FIG. 5, by upper and lower spring fingers 105, 106. These fingers, as best shown in FIG. 9, are in the form of spring metal strips having a slight bow or edgewise curvature between their front and rear ends. Each has a hole 109 extending transversely therethrough near its rear end for reception of a pivot pin 49 which, as shown in FIG. 5, serves both to secure the finger against longitudinal displacement and to journal it for vertical pivoting movement. At its front end, each finger has an arm 110 extending forwardly beyond its main body portion and defining one side of a forwardly open recess 111 therein. The oppositely facing edges of their main body portions are also cut away to form a rearwardly presenting shoulder 112 on each finger, at a distance somewhat forwardly of midlength thereof. These feed spring fingers are disposed laterally opposite the flat side face 113 of the housing 8, being retained there-against at their rear ends by the sidewall 114 of the butt 3 and the rear end of a longitudinally extending flexible strip 115 which serves as a cover for the outboard sides of the fingers. Intermediate their ends, as best shown in FIG. 11, the fingers 105, 106 and their cover strip 115 underlie oppositely disposed arms 116 and 117 projecting from a lateral extending boss 118 on the bolt and hammer spring retaining nut 64. Thus, during retraction of the bolt, the arms 116, 117 allow the fingers to swing laterally outward about their rearward ends; and, during return movement of the bolt, the fingers and their cover strip are cammed back toward the housing by the arms 116, 117.

Buffer Locking Spring The laterally projecting bolt nut boss 118 and the manual operating handle 7 both extend through a horizontal slot in the side of the housing rear counter bore 19, and each also extends between the feed spring fingers. Biasing pivotal movement of the fingers into slidably embracing engagement with the manual operating handle is a buffer locking spring 119, best shown in FIGS. 7 and 22. This spring has a vertically extending flat section 120 adapted to abut against the laterally outward face of the feed spring cover strip. Its upper and lower ends are reversely bent to form oppositely facing U-shaped sections 121 and 122, for loosely embracing the respective upper and lower edges of the cover strip and the feed spring fingers, and adjacent laterally outward facing U-shaped sections having their vertically innermost walls 123, 124 extended for insertion into the respective forwardly open recesses 111 in the feed spring finger trays. FIG. 7 shows the interrelationship of the various portions of this buffer locking spring 119 with the feed spring cover 115 and feed spring fingers 104, 105. As shown therein, the fingers 104, 105 are in their vertically spread apart position, forcing the walls 123, 124 of the locking spring into substantially horizontal planes, since the position of the manual operating handle 7 is forward of the finger shoulders 112 (FIG. 9). When the buffer member is moved rearwardly, these fingers remain thus spread apart until the manual operating handle clears the shoulders 112, at which point the locking spring 119 draws the fingers vertically toward each other to position the shoulders 112 in blocking relation with the manual operating handle so as to arrest return movement of the buffer member.

Manual Operating Handle This manual operating handle, as best seen in FIGS. 14 and 15, has a curved forwardly presenting face 125 which is interrupted at its inboard end by a slot 126 extending vertically thereacross, and by angled vertically spaced cam faces 127 adjacent its outboard end. The slot 126 serves to prevent laterally outward swinging movement of the feed spring fingers during retraction of the bolt until the bolt ribs 38, 39 strike the buffer member flange 81, moving the buffer member a further distance rearwardly. Such further rearward movement of the buffer member disengages the feed spring fingers from the slot 126 and allows them to swing laterally outward with retraction of the bolt. Such initial outward swinging movement of the fingers operates only to shift the blocking interengagement of the finger shoulders 112 from the slof 126 on the manual operating handle to the adjacent portion of its forwardly presenting face 125, however, and return movement of the buffer is delayed while such outward swinging movement of the fingers continues until their shoulders 112 reach the cam faces 127 on the manual operating handle. At that point, the buffer member begins rapidly moving forward under the biasing force of its spring 26, the faces 127 acting to cam the fingers to their vertically spread apart positions shown in FIG. 7, against the biasing force imposed by the locking spring 119.

Feed Trays The upper and lower feed trays and 6 are identical, the upper being inverted relative to the lower. Each, as best shown in FIG. 21, has a flat rectangular main body portion 128 with front and rear side flanges partially cut away to provide bolt rib clearance recesses with oppositely facing shoulders 129, 130. These shoulders serve as stops engagable by the bolt ribs to limit the stroke of the trays in their reciprocatory movement transversely of the gun. The side flanges are also cut back at their receiving ends to provide inclined ramps 131, which in the case of the lower tray serve to elevate the ammunition belt (FIG. 37) during operation of the gun by camming the successive cartridges upwardly to the proper height for passage between the trays. Lanced out from the main body portion 128 of each tray is a flexible pawl 132 which drivably interengages successive links of the ammunition belt during the ejection and feed stroke, and ratchets over the links during the return stroke. At its end nearest the stop shoulder 129 the main body portion 128 of each tray is reversely bent to form a U-shaped recess 133 extending longitudinally thereacross, for reception of the forwardly extending arm 110 of its associated feed spring finger. These recesses 133 have sufficient vertical depth to accommodate the previously described vertical pivoting movement of the fingers which accompanies the rearward and return movements of the buffer member. As shown in FIG. 6, the upper tray 5 is slidably interposed between the upper rib 38 on the bolt and the upper wall 89 of the housing slot 48, and the lower tray is slidably interposed between the lower bolt rib 39 and the bottom wall 91 of this housing slot. During the ejection and feed stroke, which accompanies the opening or rearward movement of the bolt, both trays swing laterally outward with the forward ends of the feed spring fingers, the broken line 134 in FIG. 5 representing the laterally outward position of the tray at the end of such stroke.

Power Cylinder Mounting The gas power cylinder 18, as best shown in FIG. 10, has an integral mounting ring 140 connected thereto near its forward end by a depending boss 141. The bore 142 of this ring has a close slip set on the annular peripheral surface 133 of the barrel 1 and, as shown in FIGS. 4 and 5, is clamped against a shoulder 144 at the rear end of this annular surface by a retainer nut 145 threadedly engaging the barrel. The preassembly of the power cylinder and barrel is effected before the barrel is inserted into the housing counter bore 9. Referring to FIGS. 16 and 17, it will be seen that the housing 8 has a front counter bore 146 for accommodating the outer periphery of the power cylinder mounting ring 140, and that the front end of the housing has longitudinally extending cut outs 147, 148 in its upper and lower walls. Each of these cut outs extends rearwardly through the snap ring groove 149. In the gun as assembled for right handed operation, the boss 141 extends through the upper cut out 147.

Barrel Retaining Ring The snap ring 11, as shwon in FIG. 12, has the inner periphery of its annular body portion relieved by a series of notches 151 so that in the event a malfunction in the operation of the gun creates an undue endwise force against the barrel the remaining inner peripheral portions 152 of the ring will shear off, allowing the barrel to shift forward. During installation the ring is slipped over the barrel 1 and contracted into the barrel 10 groove 149 by pressing the ring tabs 154 toward each other. When the barrel is placed in the housing, the tabs are then allowed to swing into abutment with "the sides of the upper cut out 147 in the housing.

Trigger Guard and Hand Grip Mounting The trigger guard and hand grip 4 is formed integrally with the longitudinally extending wall 102 on which the latch actuating cam member 93 is slidably supported, and is secured by providing the upper edges of its opposite sidewalls 155, 156 (FIG. 4) with inturned flanges 157, 158 (FIGS. 6 and'7). These flanges project into L-shaped grooves 159, (FIGS. 16, 17 and 18) in the bottom of the housing. Assembly of the trigger guard and hand grip to the housing is effected by endwise insertion of the flanges into these housing grooves. A like set of grooves 159 and 160 are provided in the upper outer wall surface of the housing, but are not used in the gun as assembled for right handed operation.

Triggering Mechanism Mounted for longitudinal movement in the trigger guard and hand grip is a trigger 161, shown in'its released or forwardmost position in FIG. 4. The opposite sidewalls of the trigger guard and hand grip support a cross shaft 162 with which a generally trapezoidal shaped tumbler 163 is rotatable in the path of the trigger, so that when this tumbler is rotated from its position in FIG. 4 to the so-called safety" position shown in FIG. 24 the forward end 164 of the tumbler moves into blocking relation with a shoulder 165 on the trigger, preventing depression, i.e., rearward movement, of the trigger. As'best shown in FIG. 25, the main body portion of the trigger is generally in the form of an L- shaped plate, the rear leg of which is formed with two laterally projecting bosses having vertical bores 1-66 and 166 extending therethrough, and the upper edge of the main body portion between the bosses is cut away to provide a rearwardly facing shoulder 167 a short distance forwardly of the bores 166, 166'. The left side bore 166 is not used in the gun as assembled for right handed operation, but the left bore 166 is used to journal the longer leg 168 (FIG. 26) of a generally J-shaped trigger rod actuator 169.

As shown in FIG. 4, a light coil spring 170 encircles this leg and serves to bias the actuator downwardly of the trigger, the spring 170 having its upper end abutting the boss on that side of the trigger and its lower end abutting a retainer clip on the lower end of the leg 168. Coaxial with the shaft 162 are square section hubs 171, 171', which are formed integral with the tumbler 163 and extend laterally from opposite sides thereof (FIG. 28), and wrapped around the left side hub 171 so as to rotate with the tumbler is one end of a leaf spring 172 whose opposite or free end underlies the lower end of the actuator leg 168. This leaf spring 172 is stronger than the light coil spring 170; and, with the trigger and tumbler in their positions shown in FIG. 4, the actuator is held upwardly, in abutment with the underside of the bolt latch finger 83, by the leaf spring 172. In this partially elevated position of the actuator, its shorter leg 173 (FIG; 26) has its lower end terminating slightly below the upper edge of the rear face 174 (FIG. 25) of the trigger. The trigger rod 29, as shown in FIG. 4, has its forward endabutting the rear face of the actuator, so that upon depressing the trigger both the actuator and the trigger rod move rearwardly with the trigger. Such rearward movement of the trigger rod causes the ramp surfaces 33, 34 (FIG. 8) at its rear end to cam the front sear plate 69 upwardly, releasing the hammer 61 to strike the firing pin 55, firing the gun. At the same time, the rearward movement of the actuator from under the latch finger 83 allows the leaf spring 172 to further elevate the actuator to the position shown in FIGS. 27, 28 and 29, wherein the shorter leg 173 thereof lies adjacent the rear face of the latch finger. The actuator then remains in that position, while the trigger is held depressed, until the latch actuating cam member 93 (FIG. 8) rotates the latch 47 to its bolt released position. In such bolt released position of the latch, its latch finger 83 is withdrawn from its position in front of the actuator, and the front sear plate 69, under the force of the upper sear spring 71, returns to its lower position, its ramp face 77 camming the trigger rod forwardly to its initial position. In so doing, the forward end of the trigger rod causes the short leg of the actuator to swing forwardly against the shoulder 167 on the trigger. This latter position of the actuator, as illustrated in FIG. 30, is in the path taken by the latch finger 83 during its return movement; hence during such return movement the actuator is sweptI-back to its position shown in FIGS. 27, 28 and 29, and the trigger rod is again shifted rearwardly to effect refiring of the gun. This triggering action just described takes place with the gun in its so-called full automatic mode of operation, and continues until the trigger is released, or the ammunition belt (FIGS. 36 and 37) has passed entirely through the gun. The tumbler 163 is also rotatably adjustable to an intermediate position for operation of the gun in the so-called semi-automatic mode in which successive firings each require a redepression of the trigger. Such position of the tumbler is shown in FIG. 31, wherein the free end of the leaf spring 172 is sufficiently lowered to enable the light coil spring 170 to retract the actuator so that its short leg extends down between the rear end bosses of the trigger. In such lowered position, the rear face of the trigger blocks the actuator from rotation in the bore 166, with the result that the actuator effects rearward movement of the trigger rod when the trigger is depressed.

Sear Mechanism The front and rear sear plates 69 and 70 are best shown in FIGS. 32 and 33, and their action in limiting each depression of the trigger to effect a single firing of the gun in such semi-automatic mode" of operation is illustrated diagrammatically in FIGS. 34a through 34d. FIG. 34a represents the condition prior to depression of the trigger and shows both sear plates held in their lowered position by the upper spring 71, the hammer latching face 68 being engaged by the edge 75 of the front sear plate 69, and the trigger rod 29 in its forward position. Upon depression of the trigger, the trigger rod moves rearwardly against the lower ramp face 77 of the front sear plate, forcing the front sear plate upwardly to its position shown in FIG. 34b, and releasing the hammer. Such upward movement of the front sear plate deflects the upper spring 71 upwardly, allowing the weaker lower spring 72 to elevate the rear sear plate 70 for latchably engaging the hammer latching face 68 when the hammer 61 (FIGS. 4 and is again driven rearwardly by the retracting bolt 36 after the gun fires. FIGS. 340 shows the hammer latching face 68 engaged by the edge 76 of the rear sear plate, preventing refiring of the gun pending release and redepression of the trigger. Upon release of the trigger, the upper spring returns both sear plates to their lower position shown in FIG. 34d, causing the hammer latching face 68 to be released by the edge 76 of the rear sear plate and to be again retained by the edge of the front sear plate, and the lower ramp face 77 of the front sear plate to cam the trigger rod and trigger forwardly to their original position.

Mode and Safety Lever Manually operable means for rotatably setting the tumbler 163 in either the safety position (FIG. 24), the semi-automatic mode (FIG. 31) or the full automatic mode (FIG. 4), is provided in the form of a finger lever on the left side of the trigger guard and hand grip 4 and suitablly keyed to the adjacent end of the shaft 162 with which the tumbler is rotatable. This finger lever is shown in solid lines in FIG. 35 with its indicating end 176 turned to the full automatic mode setting, and in dashed and dash-dot lines with it turned to the semi-automatic mode and safety settings, respectively.

Ammunition Feed and Ejection Referring now again to FIGS. 16 and 18, the transverse slot 48 in the housing opens forwardly into laterally transverse openings 176, 176' whose respective upper and lower walls 177, 178 and 177, 178 are tangent to the bolt bore 35 and extend forwardly into the barrel receiving counter bore 9. When the bolt retracts a spent cartridge from the chamber 13 (FIGS. 4 and 5) after each firing of the gun, such cartridge is drawn back into the aligned loop of the ammunition belt link with which it was previously carried into the housing slot 48, and is then ejected through the right hand end of slot 48 by the feed trays 5 and 6 as they draw the next live round into position for chambering by the bolt. The transverse opening 176 in the left side of the housing accommodates passage of the bullet end of the round into the housing with the feed trays.

FIGS. 36 and 37 illustrate diagrammatically the movement of the ammunition belt between the upper and lower feed trays 5 and 6 which are indicated in broken line. The belt consists of successive links, each comprising a pair of axially spaced and aligned loops 179 and 180 which adjacent ends are connected at one side to the opposite ends of a parallel loop 181. The axially spaced loops 179, 180 of each link loosely embrace the opposite ends of the parallel loop 181 of the next adjacent link and are retained in axial alignment therewith by a shell cartridge 37. Each loop 179, 180 and 181 is part circular in transverse section and the opposite sides thereof form upwardly and downwardly extending ears 182 and 183 which accommodate reciprocation of the bolt ribs therethrough during chambering and retraction of the cartridges. As best seen in FIG. 37, the sides 184 and 185 of these ears on each of the axially spaced loops 179, 180 are engagable by the pawl 132 of the feed tray, for effecting movement of the cartridge therein into alignment with the bolt during the feed and ejection stroke represented by the arrow 186 in FIG. 36. As shown in FIG. 36, the cartridges extend endwise beyond the remote ends of the loops 179, 180 and have their ends terminating fore and aft of the side flanges of the trays; whereby during each return stroke of the trays, represented by the arrow 187, the inclined ramps 131 on the receiving ends of these flanges of the lower tray 6 cam under the end of the next succeeding cartridge. This camming action elevates such next succeeding cartridge to the proper level for passage between the trays and, in so doing, serves to pull the trailing portion 188 of the belt upwardly toward the gun in the direction of the arrow 189 in FIG. 37. During the ejection and feed stroke, the spent cartridge 190 is carried outwardly of the gun by the same embracing link loops with which it entered as a live shell 14.

Housing and Spring Chamber Subassembly As best shown in FIG. 11, the upper and lower spring chambers 24 and 25 are of oppositely presenting channel-like shape in transverse section and their respective sidewalls terminate within the longitudinal slots 191, 192 in the rear counter bore of the housing. The outer sidewalls of the spring chambers and the housing, except the flat side face 113 of the housing, are encased in a plastic outer shell 193 which extends forwardly from the butt 3 to the external shoulder 194 (FIG. 16) on the housing. This shell is permanently bonded to the housing and spring chambers and effects a rigid subassembly of those parts of the gun, and the butt 3 may be secured thereto by suitable manually releasable clip means (not shown).

Operation Although the operation of the gun should be clear from the previous description of the various parts and their interrelation, a brief review of the principal action which takes place during a complete firing cycle will now be given, in their order of sequence. Firing When the trigger 161 is depressed, the trigger rod 29 shifts rearwardly, elevating the front sear plate 69, and releasing the hammer latching face 68. The hammer spring 65 thence drives the hammer 61 forwardly against the firing pin 57, forcing it forwardly to detonate the live cartridge 37 in the firing chamber 13. The gas pressure from the resulting explosion is applied through the gas port into the forward end of the power cylinder 18, driving its piston 22 and the buffer member rearwardly and compressing the bolt return spring 26 against the butt 3, the bolt retracting spring 80 against the nut 64 on the rear end of the bolt 36, and the cam actuating spring 28 against the rear end wall of the spring chamber 27. The rearward force on the cam actuating member 93 due to such compression of its spring 28 is insufficient for the cam nose portion 94 to cam away the latch finger 83 and thereby rotate the latch, however, because the latch is frictionally clamped rearwardly against the housing by the bolt rib with sufficient force of the gas explosion pressure to restrain rotation of the latch. The three springs 26, 80 and 28 yield sufiiciently to allow the buffer member to move far enough rearwardly for the feed spring finger shoulders 112 to latchably engage in the slot 126 on the front of the manual operating handle 7, the buffer cocking spring 119 pivoting the upper and lower feed spring fingers 105 and 106 vertically toward each other about their rear ends to effect such latching engagement of the manual operating handle by the shoulders 1 12. Bolt Unlocking When the shell 14 leaves the forward end of the barrel 1, the gas pressure and resultant rearward thrust on the bolt 36 is sufficiently relieved that the force of the compressed cam actuating spring 28 is then effective to shift the retainer 27 and cam member 93 rearwardly, causing the cam nose portion 94 engaging the latch finger 83 to rotate the latch to its bolt released position. The bolt is then retracted by its spring 80. With the gun operated in the full automatic mode" (finger lever 175 on the side of the trigger guard and hand grip 4 in its solid line position shown in FIG. 35), such rotation of the latch also allows the leaf spring 172 to elevate the trigger rod actuator 169 which, in turn, allows the sear upper spring 71 to move both the front and rear sear plates 69 and 70 downwardly, the front sear plate camming the trigger rod 29 forwardly and swinging the short leg 173 of the trigger rod actuator forwardly against the shoulder 167 on the trigger 161.

Extracting As the bolt retracts, the upper and lower lugs 42 on the forward ends of its ribs 38, 39, which are engaged with the extracting groove 44 on the rear end of the spent cartridge, extract such spent cartridge from the firing chamber back into the ammunition belt loops it previously occupied. When the rear ends of the bolt ribs strike the buffer member flange 81 the buffer member is further retracted sufficiently to allow the feed spring fingers'to swing laterally far enough to shift their shoulders 112 onto the forwardly presenting face 125 of the manual operating handle 7. When the rear end of the counter bore 60 in the bolt strikes the hammer 61, the hammer is driven rearwardly, to be recocked by one of the sear plates 68, 70. With the gun operated in the semi-automatic mode (finger lever l75'having its indicating end 176 extending forwardly, in the dashed line position shown in FIG. 35), the hammer latching face 68 is initially engaged by the rear sear plate 70, pending release of the trigger, and subsequently by the front sear plate when the trigger is released. With the gun operated in the full automatic mode, the rear sear plate 70 is ineffective to cock the hammer because the trigger rod 29 is automatically released to return to its forward position when the latch 47 releases the bolt, the latch finger 83 moving out from in front of the actuator 169 and allowing such return movement of the trigger rod before the hammer is driven rearwardly by the bolt.

Ejecting and Feeding As the bolt retracts, the arms 1 16 and 117 on the bolt spring retainer nut 64 allow the feed spring fingers 105, 106 to swing laterally outward,

forcing the feed trays 5 and 6 at their forward ends to shift the ammunition belt loops 182, 183 containing the spent cartridge toward the right (as viewed in FIG. 5), and bringing the next round in the ammunition belt into position axially of the firing chamber. When the shoulders 112 on the feed spring fingers reach the cam faces 127 on the manual operating handle 7, bolt return spring 26 is enabled to return the buffer member 20 fully to its forward position, these cam faces 127 wedging the feed spring fingers vertically apart and restressing the buffer locking spring 119.

Chambering and Locking The forward movement of the buffer member causes its flange 81 to engage the rear ends of the bolt ribs and return the bolt to its forward position, chambering the ammunition round in the chamber 13. Such forward movement of the bolt causes the arms 116 and 117 on the bolt spring retainer nut 64 to cam the feed spring fingers back against the flat side 113 in the housing, forcing the feed trays to shift to the left (as viewed in FIG. 5). During such return stroke of the trays, the pawls 132 thereof ratchet over the link loops 182, 183 of the cartridge 37 in the next succeeding round in the ammunition belt, and the ramp faces 131 on the lower tray 60 cam the second succeeding round upwardly to the proper height for subsequent advancement toward the gun during the next ejecting and feed stroke of the trays. During the forward movement of the buffer member its lower arm 21 engages the arm 98 on the latch actuating member 93, returning it to its forward position, determined by the arms 98 and 96 thereof reaching the forward ends of the slots 103 and 100, respectively, in the lower spring chamber 25.

Bolt Locking During such forward movement of the latch actuating cam member its nose portion 94 disengages the finger 83 on the latch 47, allowing its return spring 88 to rotate the latch back to its bolt locked position when the notches 45, 46 on the bolt ribs 38, 39 again clear the latch for such rotation. When the gun is operated in the full automatic mode, such rotation of the latch to its bolt locking position causes the latch finger 83 to rotatably sweep the trigger rod actuator 169 back to its transversely extending position, shifting the trigger rod 29 to elevate the front sear and refire the gun.

DISASSEMBLY AND REVERSIBILITY OF PARTS The gun as described may be disassembled and reassembled for operation most convenient to a left handed user. Such disassembly may be initiated by removing the snap ring 11, barrel 1 and the trigger guard and hand grip 4 from the front portion of the housing, and separating the butt 3 from the rear end thereof. The various parts, including the latch actuating cam member 93, latch 47, retainer 27, trigger rod actuator 169, leaf spring 172 and coil springs 26 and 28 may then be removed. In reassembling the gun for a left handed user, the barrel and snap ring are installed with the power cylinder 18 aligned with the spring chamber 25. The latch actuating cam member 93 is installed, turned end for end, so that its arm 96' engages in the opening 101 in the retainer 27. This retainer and cam member, along with the spring 28, are installed in the spring chamber 24; and the latch 47, with its previously forwardly presenting face to the rear, is installed on the bolt. The trigger guard and hand grip 4 is inserted in the housing grooves 159, 160' the latch finger actuator 169 is inserted in the bore 166 of the trigger 161 and the leaf spring 172 is installed on the hub 171' of the tumbler 163. The buffer is installed with the piston 22 and the trigger rod 29 piloted in the through holes in the buffer arms 21 and 21, respectively, and the springs 26 and 28 are placed in the spring chambers and 24, respectively.

As thus reassembled the ammunition belt feeds into the right side of the gun, and the feed spring fingers 105, 106, buffer locking spring 119 and manual operating lever 7 are located on the left side for more convenient operation by a left handed user.

Although the invention as described and illustrated in the drawings represents a preferred embodiment, it is appreciated that various changes in the parts and their arrangement may be made without departing from the spirit and scope of the invention as set forth in the following claims.

I claim:

1. In a gun having a firing chamber, a retractable bolt for closing said chamber, spring means including a first spring for retracting the bolt and a second spring for returning the bolt to its chamber closing position, buffer means movable against both said springs by the pressure of the gases of explosion, releasable latch mans for delaying retraction of the bolt pending dissipation of said gas pressure, and means operative to release said latch means in response to dissipation of said gas pressure, said last named means including cam means and a third spring interposed between said cam means and said buffer means.

2. In the gun of claim 1, said buffer means and bolt being in telescopic relation with each other, and said first spring means comprising a coil spring telescopically interposed between the buffer means and bolt.

3. In the gun of claim 2, a housing slidably supporting the bolt and buffer means, and spring chambers extending longitudinally of said housing and enclosing said second and third springs.

4. In the gun of claim 3, said bolt carrying a firing pin and a hammer movable into striking engagement with the firing pin, releasable sear means for retaining the hammer during return movement of the bolt to its chamber closed position, and hammer spring means for propelling the hammer into striking engagement with the firing pin upon release of said sear means, said hammer spring means being connected to the bolt for applying bias thereto during said return movement of the bolt.

5. In a gun having a retractable bolt, bolt guiding means, said bolt and guiding means each having a noncircular cross-section preventing rotation of the bolt in the guiding means, a rotary latch embracing the bolt and journalled for rotation relative to the bolt and guiding means, said latch having a non-circular aperture registerable with said non-circular cross section of the bolt to accommodate retraction of the bolt therethrough when the latch is rotated to its bolt releasing position, spring means interposed between said guiding means and the latch and rotatably biasing the latch to its bolt retaining position in which said aperture is out of registry with said bolt cross section, and cam means operative to rotate the latch to its said bolt releasing position against the bias of said spring means in response to firing of the gun.

6. In the gun of claim 5, said non-circular cross section of the bolt comprising two oppositedly disposed part-circular sections interconnected by radially extending ribs extending longitudinally of the bolt, each of said ribs having a transversely extending slot intermediate the ends thereof, said slots accommodating rotation of the latch between its bolt retaining and bolt releasing positions.

7. In a gas fired machine gun having a barrel with a bore and a firing chamber at the rear end of said bore, a housing supporting the rear end of said barrel and extending rearwardly therefrom, a retractable bolt for opening and closing said chamber, said housing having a bore slidably supporting said bolt and a counter bore extending rearwardly from said bolt bore, the sidewalls of said housing having slots extending longitudinally of said counter bore, generally U-shaped spring chambers secured to the housing opposite said slots, a generally tubular shaped buffer member slidably fitting said counter bore and having arms projecting perpendicularly thereof at its front end, said arms extending through slots into said spring chambers, a shoulder butt closing the rear end of said counter bore and spring chambers a cylinder extending forwardly of one of said chambers, a piston slidably fitting said cylinder, the rear end of said piston being in abutment with the buffer member in said one spring chamber, said barrel having a gas port extending laterally outward from its bore adjacent the firing chamber, said cylinder having a passage connecting its forward end with said port, a coil compression spring in each of said spring chambers, said springs being in abutment at their forward ends with said buffer member arins, said spring in said one spring chamber being in abutment at its rear end with said shoulder butt, a spring retainer slidably mounted in the other of said spring chambers and abutting the rear end of the other of said springs, a rotary latch for releasably retaining the bolt in its chamber closed position, a cam member connected to said spring retainer, said latch having an actuating finger drivable by said cam member to release the bolt, said bolt having a nut slidably fitting the internal walls of the buffer member, external ribs on the bolt spaced forwardly thereof from said nut, said buffer member having an internal flange at its front end, said flange being abuttable with the rear ends of said ribs, and a coil. compression spring surrounding the bolt within the buffer member and having its opposite ends abutting said flange and nut, respectively.

8. In a gun having a bore, a firing chamber at the rear end of said bore, a bolt actuatable to open and close said chamber, and means for actuating said bolt including a gas port connected to the bore, a cylinder extending longitudinally of the gun and connected at its forward end to said port, and a piston operatively connected to the bolt and movable rearwardly in said cylinder in response to gas pressure developed at said port upon firing of the gun, spring means yieldably opposing said rearward movement of the piston, said spring means including a first spring biasing the bolt to its chamber open position, a releasable latch engagable with the bolt to prevent its movement in response to the biasing force of said first spring pending release of the latch, and cam means actuatable to release said latch, said spring means including a second spring for actuating the cam means upon dissipation of said gas pressure, said second spring having one end movable with the piston and its other end connected to said cam means.

9. In the gun of claim 8, a buffer member movable with the piston and having a lost motion connection with the bolt accommodating rearward movement of the buffer member pending release of the bolt by said latch, said first spring being operable upon release of the bolt by the latch means to take up the lost motion of said connection by actuating the bolt to its chamber open position, said spring means including a third spring yieldably opposing said rearward movement of the buffer member and operable to return the bolt with the buffer member to the chamber closed position of the bolt.

10. In the gun of claim 9, a housing extending rearwardly of said chamber and cylinder, a spring finger secured at one end for pivot movement relative to the housing and having a shoulder intermediate its ends, said buffer member having a manual operating lever engagable by said shoulder, and a buffer cocking spring pivotally biasing the finger against the lever to effect its latching engagement by said shoulder.

11. In a gun having a barrel with a bore and a firing chamber at the rear end of said bore, a bolt for closing said chamber, said bolt being retractable axially of said bore to open said chamber, a releasable latch for retaining said bolt in its chamber closed position, a buffer member movable rearwardly relative to the bolt while the bolt is retained in its cha'imber closed position by the latch, spring means yieldably opposing rearward movement of the buffer member including a first spring reacting against the bolt and operative to retract the boltwhen the latch is released, and means for moving the buffer member rearwardly against said spring means in response to the gas pressure developed in the chamber during firing of the gun, said last named maens including a gas port in said bore, a cylinder extending longitudinally of the gun and having its forwardend connected to said port, a piston connected to the buffer member and extending into the rear end of said cylinder, and a cam member movable to release said latch, said spring means including a second spring reacting against the cam member and operative to move the cam member to release the latch in response to dissipation of said gas pressure.

12. In the gun of claim 11, said buffer member having a lost motion connection with the bolt accommodating rearward movement of the buffer member while the bolt is retained in its chamber closed position, said last motion being taken up during retraction of the bolt by said first spring when the latch is released, said spring means including a third spring, fixed reactionmeans for said third spring, said third spring being operative to return the bolt with the buffer member to the chamber closed position of the bolt and the cam member and piston to their initial positions, and a latch spring operative to return the latch to its bolt retaining position when the bolt returns to its chamber closed position.

13. In the gun of claim 12, a firing pin telescopically slidable in the forward end of the bolt, a hammer telescopically slidable in the rear end of the bolt, a spring interposed between the hammer and the rear end of the bolt for biasing the hammer into striking engagement with the firing pin, said hammer having a rearwardly extending stem, and sear means for releasably interengaging said stem during retraction of the bolt.

14. In the gun of claim 12, said sear means including a sear plate movable in a plane perpendicular to said stem, said sear plate having an aperture spaced from one end thereof, said stem being receivable within said aperture and having a forwardly presenting face engagable with the sear plate at one edge of said aperture, a sear spring biasing said sear plate perpendicularly of the stem in the direction to engage said edge with the stern face, means for disengaging said sear plate edge from said stem face including a longitudinally shiftable rod extending longitudinally of the gun, the rear end of said rod being in abutment with said sear plate end, one of said sear plate end and said rod end having a ramp surface facing the other.

15. In the gun of claim 14, means for shifting said rod rearwardly to disengage said sear plate edge from said hammer stem face, including a trigger depressable toward the forward end of said rod, said trigger having a rearwardly presenting end face, a shoulder spaced forwardly of said end .face and a bore extending therethrough adjacent said end face, an actuator having a first leg extending through said bore and a second leg disposed laterally of said first leg, said second leg being in abutment with the forward end of said rod, said actuator being shiftable axially of said trigger bore between a first position and a second position, said actuator in said first position having its said second leg abuttable by said trigger end face whereby said trigger rod is shifted rearwardly by depression of the trigger, said actuator in said second position having its said second leg abuttable by said trigger shoulder when said trigger is depressed, said latch having a finger operable during movement of the latch to its bolt retaining position to shift said second leg rearwardly from said trigger shoulder whereby said rod is shifted rearwardly in response to said latch spring returning said latch to its bolt retaining position.

16. In the gun of claim 15, means for selectively shifting said actuator to said first and second positions, including a rotatable tumbler, a leaf spring having one end disposed opposite the extended end of said actuator first leg and its other end fixed to rotate with said tumbler, whereby in response to rotation of said tumbler in one direction said leaf spring biases the actuator towards its said second position, and a coil spring interposed in thrust between said trigger and the extended end of said actuator first leg, whereby in response to rotation of the tumbler in the opposite direction said coil spring biases the actuator toward its said first position.

17. In the gun of claim 15, said trigger having a second shoulder, said tumbler having an end movable into abuttable relation with said second shoulder by continued rotation of the tumbler in said opposite direction after said actuator has shifted to its said first position, whereby depression of the trigger is blocked by said tumbler.

18. In a gun having a barrel with a bore and a firing chamber at the rear end of said bore, a bolt for closing said chamber, said bolt being retractable axially of said bore to open said chamber, a releasable latch for retaining said bolt in its chamber closed position, a buffer member movable rearwardly relative to the bolt while the bolt is retained in its chamber closed position by the latch, spring means yieldably opposing rearward movement of the buffer member including a first spring reacting against the bolt and operative to retract the bolt when the latch is released, and means for moving the buffer member rearwardly against said spring means in response to the gas pressure developed in the chamber during firing of the gun, said last named means including a gas port in said bore, a cylinder extending longitudinally of the gun and having its forward end connected to said port, a piston connected to the buffer member and extending into the rear end of said cylinder, said bolt having an externally cylindrical portion and diametrically opposite ribs extending forwardly of said portion, said latch having a part-cylindrical bore journalling the latch on said bolt portion when the bolt is in its chamber closed position and having diametrically opposite keyways accommodating passage of the bolt ribs therethrough when the latch is rotated to its bolt released position, a housing slidably supporting the bolt and thrustably supporting the latch against rearward movement, a latch spring rotatably biasing the latch to its bolt retaining position in which said keyways are out of alignment with the bolt ribs, said latch having a fin ger spaced from and extending transversely of the bolt, and a cam member mounted for rearward movement to shift said finger transversely of the bolt and thereby rotate the latch to its bolt released position, said spring means including a second spring reacting against the cam member and operative to impart said rearward movement to the cam member when the thrust force imposed on the latch by the gas pressure against the bolt during firing of the gun is relieved.

19. In a gun having a barrel, a firing chamber at the rear end of the barrel, a retractable bolt for closing the chamber, bolt retracting means operative in response to gas pressure developed in the barrel during firing of the gun, said retracting means including a cylinder extending rearwardly of and connected to a port in the barrel, a piston in the cylinder and spring means opposing rearward movement of the piston, said spring means being disposed rearwardly of the piston and operatively connected to the bolt, releasable latch means for retaining the bolt in its chamber closed position, cam means actuatable by said spring means upon dissipation of said gas pressure to release said latch means for retraction of the bolt by said spring means, buffer means movable rearwardly with the piston and connecting the piston to said spring means, said spring means including one spring having fixed reaction means, said buffer means having lost motion connections with the cam means and the bolt, said lost motions being taken up by the actuation of the cam means to release the bolt and the retraction of the bolt, respectively, said one spring being operable thereafter to return the buffer means, piston, cam means and bolt to their initial positions.

20. In the gun of claim 19, a firing pin, a hammer for striking the firing pin, resilient means interposed be tween the bolt and hammer for biasing the hammer into striking engagement with the firing pin, and releasable sear means retaining the hammer against movement by said resilient means during return of the bolt to its chamber closed position, said firing pin and hammer being slidably carried in opposite ends of the bolt. 

1. In a gun having a firing chamber, a retractable bolt for closing said chamber, spring means including a first spring for retracting the bolt and a second spring for returning the bolt to its chamber closing position, buffer means movable against both said springs by the pressure of the gases of explosion, releasable latch mans for delaying retraction of the bolt pending dissipation of said gas pressure, and means operative to release said latch means in response to dissipation of said gas pressure, said last named means including cam means and a third spring interposed between said cam means and said buffer means.
 2. In the gun of claim 1, said buffer means and bolt being in telescopic relation with each other, and said first spring means comprising a coil spring telescopically interposed between the buffer means and bolt.
 3. In the gun of claim 2, a housing slidably supporting the bolt and buffer means, and spring chambers extending longitudinally of said housing and enclosing said second and third springs.
 4. In the gun of claim 3, said bolt carrying a firing pin and a hammer movable into striking engagement with the firing pin, releasable sear means for retaining the hammer during return movement of the bolt to its chamber closed position, and hammer spring means for propelling the hammer into striking engagement with the firing pin upon release of said sear means, said hammer spring means being connected to the bolt for applying bias thereto during said return movement of the bolt.
 5. In a gun having a retractable bolt, bolt guiding means, said bolt and guiding means each having a non-circular cross-section preventing rotation of the bolt in the guiding means, a rotary latch embracing the bolt and journalled for rotation relative to the bolt and guiding means, said latch having a non-circular aperture registerable with said non-circular cross section of the bolt to accommodate retraction of the bolt therethrough when the latch is rotated to its bolt releasing position, spring means interposed between said guiding means and the latch and rotatably biasing the latch to its bolt retaining position in which said aperture is out of registry with said bolt cross section, and cam means operative to rotate the latch to its said bolt releasing position against the bias of said spring means in response to firing of the gun.
 6. In the gun of claim 5, said non-circular cross section of the bolt comprising two oppositedly disposed part-circular sections interconnected by radially extending ribs extending longitudinally of the bolt, each of said ribs having a transversely extending slot intermediate the ends thereof, said Slots accommodating rotation of the latch between its bolt retaining and bolt releasing positions.
 7. In a gas fired machine gun having a barrel with a bore and a firing chamber at the rear end of said bore, a housing supporting the rear end of said barrel and extending rearwardly therefrom, a retractable bolt for opening and closing said chamber, said housing having a bore slidably supporting said bolt and a counter bore extending rearwardly from said bolt bore, the sidewalls of said housing having slots extending longitudinally of said counter bore, generally U-shaped spring chambers secured to the housing opposite said slots, a generally tubular shaped buffer member slidably fitting said counter bore and having arms projecting perpendicularly thereof at its front end, said arms extending through slots into said spring chambers, a shoulder butt closing the rear end of said counter bore and spring chambers a cylinder extending forwardly of one of said chambers, a piston slidably fitting said cylinder, the rear end of said piston being in abutment with the buffer member in said one spring chamber, said barrel having a gas port extending laterally outward from its bore adjacent the firing chamber, said cylinder having a passage connecting its forward end with said port, a coil compression spring in each of said spring chambers, said springs being in abutment at their forward ends with said buffer member arms, said spring in said one spring chamber being in abutment at its rear end with said shoulder butt, a spring retainer slidably mounted in the other of said spring chambers and abutting the rear end of the other of said springs, a rotary latch for releasably retaining the bolt in its chamber closed position, a cam member connected to said spring retainer, said latch having an actuating finger drivable by said cam member to release the bolt, said bolt having a nut slidably fitting the internal walls of the buffer member, external ribs on the bolt spaced forwardly thereof from said nut, said buffer member having an internal flange at its front end, said flange being abuttable with the rear ends of said ribs, and a coil compression spring surrounding the bolt within the buffer member and having its opposite ends abutting said flange and nut, respectively.
 8. In a gun having a bore, a firing chamber at the rear end of said bore, a bolt actuatable to open and close said chamber, and means for actuating said bolt including a gas port connected to the bore, a cylinder extending longitudinally of the gun and connected at its forward end to said port, and a piston operatively connected to the bolt and movable rearwardly in said cylinder in response to gas pressure developed at said port upon firing of the gun, spring means yieldably opposing said rearward movement of the piston, said spring means including a first spring biasing the bolt to its chamber open position, a releasable latch engagable with the bolt to prevent its movement in response to the biasing force of said first spring pending release of the latch, and cam means actuatable to release said latch, said spring means including a second spring for actuating the cam means upon dissipation of said gas pressure, said second spring having one end movable with the piston and its other end connected to said cam means.
 9. In the gun of claim 8, a buffer member movable with the piston and having a lost motion connection with the bolt accommodating rearward movement of the buffer member pending release of the bolt by said latch, said first spring being operable upon release of the bolt by the latch means to take up the lost motion of said connection by actuating the bolt to its chamber open position, said spring means including a third spring yieldably opposing said rearward movement of the buffer member and operable to return the bolt with the buffer member to the chamber closed position of the bolt.
 10. In the gun of claim 9, a housing extending rearwardly of said chamber and cylinder, a spring finger secured at one end for pivOt movement relative to the housing and having a shoulder intermediate its ends, said buffer member having a manual operating lever engagable by said shoulder, and a buffer cocking spring pivotally biasing the finger against the lever to effect its latching engagement by said shoulder.
 11. In a gun having a barrel with a bore and a firing chamber at the rear end of said bore, a bolt for closing said chamber, said bolt being retractable axially of said bore to open said chamber, a releasable latch for retaining said bolt in its chamber closed position, a buffer member movable rearwardly relative to the bolt while the bolt is retained in its chamber closed position by the latch, spring means yieldably opposing rearward movement of the buffer member including a first spring reacting against the bolt and operative to retract the bolt when the latch is released, and means for moving the buffer member rearwardly against said spring means in response to the gas pressure developed in the chamber during firing of the gun, said last named maens including a gas port in said bore, a cylinder extending longitudinally of the gun and having its forward end connected to said port, a piston connected to the buffer member and extending into the rear end of said cylinder, and a cam member movable to release said latch, said spring means including a second spring reacting against the cam member and operative to move the cam member to release the latch in response to dissipation of said gas pressure.
 12. In the gun of claim 11, said buffer member having a lost motion connection with the bolt accommodating rearward movement of the buffer member while the bolt is retained in its chamber closed position, said last motion being taken up during retraction of the bolt by said first spring when the latch is released, said spring means including a third spring, fixed reaction means for said third spring, said third spring being operative to return the bolt with the buffer member to the chamber closed position of the bolt and the cam member and piston to their initial positions, and a latch spring operative to return the latch to its bolt retaining position when the bolt returns to its chamber closed position.
 13. In the gun of claim 12, a firing pin telescopically slidable in the forward end of the bolt, a hammer telescopically slidable in the rear end of the bolt, a spring interposed between the hammer and the rear end of the bolt for biasing the hammer into striking engagement with the firing pin, said hammer having a rearwardly extending stem, and sear means for releasably interengaging said stem during retraction of the bolt.
 14. In the gun of claim 12, said sear means including a sear plate movable in a plane perpendicular to said stem, said sear plate having an aperture spaced from one end thereof, said stem being receivable within said aperture and having a forwardly presenting face engagable with the sear plate at one edge of said aperture, a sear spring biasing said sear plate perpendicularly of the stem in the direction to engage said edge with the stem face, means for disengaging said sear plate edge from said stem face including a longitudinally shiftable rod extending longitudinally of the gun, the rear end of said rod being in abutment with said sear plate end, one of said sear plate end and said rod end having a ramp surface facing the other.
 15. In the gun of claim 14, means for shifting said rod rearwardly to disengage said sear plate edge from said hammer stem face, including a trigger depressable toward the forward end of said rod, said trigger having a rearwardly presenting end face, a shoulder spaced forwardly of said end face and a bore extending therethrough adjacent said end face, an actuator having a first leg extending through said bore and a second leg disposed laterally of said first leg, said second leg being in abutment with the forward end of said rod, said actuator being shiftable axially of said trigger bore between a first position and a second position, Said actuator in said first position having its said second leg abuttable by said trigger end face whereby said trigger rod is shifted rearwardly by depression of the trigger, said actuator in said second position having its said second leg abuttable by said trigger shoulder when said trigger is depressed, said latch having a finger operable during movement of the latch to its bolt retaining position to shift said second leg rearwardly from said trigger shoulder whereby said rod is shifted rearwardly in response to said latch spring returning said latch to its bolt retaining position.
 16. In the gun of claim 15, means for selectively shifting said actuator to said first and second positions, including a rotatable tumbler, a leaf spring having one end disposed opposite the extended end of said actuator first leg and its other end fixed to rotate with said tumbler, whereby in response to rotation of said tumbler in one direction said leaf spring biases the actuator towards its said second position, and a coil spring interposed in thrust between said trigger and the extended end of said actuator first leg, whereby in response to rotation of the tumbler in the opposite direction said coil spring biases the actuator toward its said first position.
 17. In the gun of claim 15, said trigger having a second shoulder, said tumbler having an end movable into abuttable relation with said second shoulder by continued rotation of the tumbler in said opposite direction after said actuator has shifted to its said first position, whereby depression of the trigger is blocked by said tumbler.
 18. In a gun having a barrel with a bore and a firing chamber at the rear end of said bore, a bolt for closing said chamber, said bolt being retractable axially of said bore to open said chamber, a releasable latch for retaining said bolt in its chamber closed position, a buffer member movable rearwardly relative to the bolt while the bolt is retained in its chamber closed position by the latch, spring means yieldably opposing rearward movement of the buffer member including a first spring reacting against the bolt and operative to retract the bolt when the latch is released, and means for moving the buffer member rearwardly against said spring means in response to the gas pressure developed in the chamber during firing of the gun, said last named means including a gas port in said bore, a cylinder extending longitudinally of the gun and having its forward end connected to said port, a piston connected to the buffer member and extending into the rear end of said cylinder, said bolt having an externally cylindrical portion and diametrically opposite ribs extending forwardly of said portion, said latch having a part-cylindrical bore journalling the latch on said bolt portion when the bolt is in its chamber closed position and having diametrically opposite keyways accommodating passage of the bolt ribs therethrough when the latch is rotated to its bolt released position, a housing slidably supporting the bolt and thrustably supporting the latch against rearward movement, a latch spring rotatably biasing the latch to its bolt retaining position in which said keyways are out of alignment with the bolt ribs, said latch having a finger spaced from and extending transversely of the bolt, and a cam member mounted for rearward movement to shift said finger transversely of the bolt and thereby rotate the latch to its bolt released position, said spring means including a second spring reacting against the cam member and operative to impart said rearward movement to the cam member when the thrust force imposed on the latch by the gas pressure against the bolt during firing of the gun is relieved.
 19. In a gun having a barrel, a firing chamber at the rear end of the barrel, a retractable bolt for closing the chamber, bolt retracting means operative in response to gas pressure developed in the barrel during firing of the gun, said retracting means including a cylinder extending rearwardly of and connected to a port in the barrel, a piston in the cylinder and spring means opposing rearward movement of the piston, said spring means being disposed rearwardly of the piston and operatively connected to the bolt, releasable latch means for retaining the bolt in its chamber closed position, cam means actuatable by said spring means upon dissipation of said gas pressure to release said latch means for retraction of the bolt by said spring means, buffer means movable rearwardly with the piston and connecting the piston to said spring means, said spring means including one spring having fixed reaction means, said buffer means having lost motion connections with the cam means and the bolt, said lost motions being taken up by the actuation of the cam means to release the bolt and the retraction of the bolt, respectively, said one spring being operable thereafter to return the buffer means, piston, cam means and bolt to their initial positions.
 20. In the gun of claim 19, a firing pin, a hammer for striking the firing pin, resilient means interposed between the bolt and hammer for biasing the hammer into striking engagement with the firing pin, and releasable sear means retaining the hammer against movement by said resilient means during return of the bolt to its chamber closed position, said firing pin and hammer being slidably carried in opposite ends of the bolt. 